Reports the findings of a multinational collaborative study involving 3,000 breast-feeding mothers in Guatemala, the Philippines, Zaire, Hungary, and Sweden. The study, which followed a standardized methodology, was designed to show whether growth rate differences result from differences in the quality or quantity of breast milk. The study groups were deliberately selected to represent different traditions, ways of life, socioeconomic status, and nutritional background. Data were collected and analyses on the quantity of breast milk, its composition in protein and non-protein nitrogen, lactose, fat, lactalbumin and lactoferrin, vitamin A and vitamin C, and the levels of pesticides present in the breast milk. Apart from confirming the observation that lactation is independent of the nutritional state of the mother, unless this is very bad, the book presents findings of value in determining the most appropriate age to begin supplementary feeding